An herbicide is a compound which adversely controls or modifies plant growth, e.g., killing, retarding, defoliating, desiccating, regulating, stunting, tillering, stimulating, and dwarfing. The term "plant" refers to all physical parts of a plant, including seeds, seedlings, saplings, roots, tubers, stems, stalks, foliage, and fruits. "Plant growth" includes all phases of development from seed germination to natural or induced cessation of life.
Herbicides are generally used to control or eradicate weed pests. They have gained a high degree of commercial success because it has been shown that such control can increase crop yield and reduce harvesting costs.
The most popular methods of herbicide application include: preplant incorporation into the soil; in-furrow application to seeds and surrounding soil; pre-emergence surface treatment of seeded soil; post-emergence treatment of the plant and soil; and preplant seed treatment.
A manufacturer of an herbicide generally recommends a range of application rates and concentrations calculated to maximize weed control. The range of rates varies from approximately 0.005 to 10 pounds per acre (0.0056 to 56 kilograms per hectare [kg/ha]), and is usually in the range of from 0.05 to 5 pounds per acre (0.056 to 5.6 kg/ha). The term "herbicidally effective amount" describes an amount of an herbicide compound which adversely controls or modifies plant growth. The actual amount used depends upon several considerations, including particular weed susceptibility and overall cost limitations.
An important factor influencing the usefulness of a given herbicide is its selectivity towards crops. In some cases, a beneficial crop is susceptible to the effects of the herbicide. In addition, certain herbicidal compounds are phytotoxic to some weed species but not to others. To be effective, an herbicide must cause minimal damage (preferably no damage) to the beneficial crop while maximizing damage to weed species which infest the locus of the crop.
To preserve the beneficial aspects of herbicide use and to minimize crop damage, many herbicide antidotes have been prepared. These antidotes reduce or eliminate damage to the crop without substantially impairing the damaging effect of the herbicide on weed species. See, for example, U.S. Pat. Nos. 4,021,224, 4,021,229 and 4,230,874.
Identification of an antidote which safens an herbicide in crops is a highly complicated task. The precise mechanism by which an antidote reduces herbicidal crop injury has not been established. An antidote compound may be a remedy, interferent, protectant, or antagonist. As used herein, "antidote" describes a compound which has the effect of establishing herbicide selectivity, i.e., continued herbicidal phytotoxicity to weed species by the herbicide, and reduced or non-phytotoxicity to the cultivated crop species. The term "antidotally effective amount" describes an amount of an antidote compound which counteracts to some degree a phytotoxic response of a beneficial crop to an herbicide.
Tetrazolinone compounds have been found to be very effective herbicides with broad general herbicidal activity against broad-leafed and grass weeds by pre- and/or post-emergence application. The method of controlling vegetation with these compounds comprises applying an herbicidally effective amount of the compounds, usually with an inert carrier or diluent, to the area where herbicidal control is desired. However, the herbicidal tetrazolinone compounds have been found in some instances to adversely affect or interfere with the cultivation of crop plants, especially corn and soya crops. Therefore, the effective use of these herbicides for controlling weeds in the presence of such crops is further enhanced by, or may require in many instances, the addition of an antidotally effective amount of a compound, which is antidotally effective with the herbicide.
It has now been discovered that certain compounds when used in an antidotally effective amount are effective antidotes for the protection of crops, especially corn, wheat, rice and soya, from adverse herbicidal injury or the reduction of adverse herbicidal injury caused by the use of an herbicidally effective amount of a tetrazolinone compound. Therefore, it is an object of the present invention to provide compositions of tetrazolinone herbicides in combination with antidotes therefor, which compositions are useful to reduce injury to crops, especially corn, wheat, rice and soya, due to phytotoxicity of these herbicides.